In machines such as an internal combustion engine, an oil filter is used to suppress the degradation of oil. Patent Literature 1 discloses a filter medium for a bypass oil filter used in the internal combustion engine. The filter medium contains a hydrotalcite-like compound (hydrotalcite-type compound) represented by the following formula (1). According to the description of Patent Literature 1, fine particles such as the hydrotalcite-like compound have adsorbing ability of acids, alkalis to adsorb acidic substances generated in the internal combustion engine, and thus have a role to protect the oil from degradation.MgxAl2(OH)6+2x−2y(CO3)y.mH2O  (1)wherein in the formula (1), x and y are integers which satisfy 3<x<20, 0<y<2, respectively, and m represents an integer.